Hydraulic cushion assembly



9, 1966 K. F. WITT HYDRAULIC CUSHION ASSEMBLY Filed May 18, 1964 INVENOR. KENNETH F. WITT PM ATTORNEYS m on A in 7 mm mm United States Patent3,264,942 HYDRAULIIC CUSHIUN ASSEMBLY Kenneth F. Witt, Wolcott, tConnn,assignor to Witt Machine Co, inc, Waltham, Mass, a corporation ofMassachusetts Filed May 113, 1964, @er. No. 368,187 9 Claims. (Cl.9ll35) This invention relates to a remote hydraulic cushion assembly forreducing shock in a closed, hydraulic system having a double actingcylinder, a pump and flow reversal means.

In conventional hydraulic systems of this type, it has been proposed toprovide resilient spring, or air cushion means, to take up shock whenthe incompressible hydraulic fluid filling the system. is suddenlystopped by a shut-off valve, or reversed in its path by conventionalvalving. However, such expand-able or compressible resilientcompensators or accumulators tend to defeat the purpose of liquidsystems in achieving accurate control of the work.

Therefore, the work cylinders of some such systems, have sometimes beenequipped with a hydraulic cushion to reduce the shock of instantlystopping a fast moving load against the end of the work cylinder. Suchdevices usually trap the hydraulic fluid at each opposite end of itsstroke, directing the trapped fluid through a small orifice to createback pressure and decelerate the piston near the opposite ends of thecylinder.

However, there are many hydraulic systems in use which have non-cushioncylinders and the cushion cylinders, now in use, cushion only theopposite ends of the stroke, although shock occurs in the system whenthe piston is stopped, or reversed, at any location along the workcylinder.

It is the principal object of this invention to provide a hydrauliccushion in a closed, incompressible hydraulic system, remote from thework cylinder, but arranged to cushion, or dampen, the movement of thework piston when flow is stopped, or reversed, with the work piston atany location along the work cylinder.

Another object of the invention is to provide such a remote, hydrauliccushion with a double acting valve and floating ipiston such that thepiston creates instantaneous initial back pressure on the work pistonwhen flow is reversed and the back pressure is gradually diminished bythe valve.

A further object of the invention is to provide a remote hydrauliccushion having double acting throttle valve means and a floating pistonfor creating back pressure, the orifices of the throttle valve meansbeing adjustable in cross sectional area to adjust the back pressure.

Still another object of the invention is to provide a hydraulic cushionassembly having a cylindrical valve rod with, tapered, grooved endscooperable with end bores to form orifices of variable cross sectionwhereby movement of each rod end into its bore progressively diminishesflow while the corresponding movement of the other rod end our of itsbore progressively increases flow.

A still further object of the invention is to provide a closed,substantially incompressible, reversible hydraulic system with a doubleacting hydraulic cushion assembly connected in parallelism with the workcylinder of the system, the piston and throttle valves of the assemblygradually decelerating the piston of the work cylinder upon anystoppage, or direction change, of the oil to reduce shock in the system.

Other objects and advantages of the invention will be apparent from theclaims, the description of the drawing and from the drawing in which:

FIGURES l to 4 are diagrammatic views in half section of a hydraulicsystem containing the remote cushion of the 3,254,942 Patented August 9,1966 invention, and illustrating stages of the operation of the system.

FIGURE 5 is an enlarged side elevation, in half section of the hydrauliccushion assembly.

As shown in the drawing, the closed hydraulic system 29, includes asource of hydraulic fluid under pressure, such as the positivedisplacement, constant delivery hydraulic pump 21, and the double actingcylinder and piston motor 22, the cylinder 23 thereof being designatedthe work cylinder and the piston 24 thereof being designated the workpiston. The work piston 24 has the usual piston rod 25, shown as beingconnected to a load 26 upon which it is to perform work, and the workpiston 24 is capable of exerting thrust in both axial directions in theconventional manner. The system 20 also includes the conventional fluidreservoir 27, the conventional flow control valves 28 and 29 of thevariable orifice type for regulating the speed of travel of piston 24and the hydraulic conduits 32, 33, 34, 35, 36 and 37 all arranged in theconventional manner.

The system 20 also includes control mechanism 38, in the form of a fourway, three position valve, one position advancing the rod 25, oneposition retracting the rod 25, and one position being neutral with allports blocked to hold the rod 25 stationary. The pump 21, in thedrawing, is of the unidirectional flow type, changes in direction beingaccomplished by the means 38, but the system illustrated is exemplaryonly and not intended to limit the invention to any particular type, orlocation, of the control mechanism.

The double acting cylinder 23 is of the non-cushion type and there areno energy accumulators or compressible shock absorbers in the system 20,since it is in such an incompressible system that the invention isparticularly useful.

The pump 21 includes a conventional pressure relief valve and thereservoir 27 includes a conventional air vent 31 to the atmosphere.

The remote hydraulic cushion assembly 40 comprises the double actingcushion cylinder 41, which is connected into the system 20, by hydraulicconduit means 42 consisting of conduits 43 and 44 and the ports 45 and46 at each opposite end 47 and 43 of the cylinder. The double actingcylinder 41 is thus mounted in parallelism with the work cylinder 23 sothat the end 47 of cylinder 41 is connected to the corresponding end 50of cylinder 23 and the other end 48 of cylinder 41 is connected to thecorresponding end 51 of cylinder 23. If the cylinder 41, were merely anopen passage, it would constitute a bypass around the cylinder 23 andpiston 24 so that back pressure would substantially equal forwardpressure on piston 24 and any effective work by the piston would dependon the relative cross sectional areas of the parts.

However, cylinder 41 is not such an open passage and is provided with acentrally disposed, axially extending piston chamber 52 of predeterminedlength and diameter, the diameter being for example, about one third thediameter of the work cylinder. Conveniently, each end 47 and 48 ofcylinder 41 is identical and consists of an end cap 53 or 54 threadedlyconnected at 55 and 56 to a cylindrical shell 57 and each end capincludes a cylindrical axial bore 58 or 59. Each bore 58 or 59 is closedat the outside end there being adjusting means 61 in the form of anadjusting screw 62 or 63 threaded at 64 or 65 in the end cap for apurpose to be described hereinafter. The inside end of each bore 58 or59 opens into the piston chamber 52 and connects one end of the chamberwith the adjacent port. Suitable O ring, or other type seals, 66 areprovided to make the cylinder a fluid tight unitary assembly.

Throttle valve means 70 is provided consisting of the double acting,cylindrical, valve rod 71 which extends a axially of the cylinder 41 inthe piston chamber 52 with each opposite end 72 or 73 thereof axiallyslidable in one of the cylindrical bores 58 or 59. Orifice forming means74 at each opposite end 72 or 73 of valve rod 71 includes an annularseries of tapered grooves such as 75 or 76, each groove being deep atthe outside end of the rod so that in cooperation with the bore, thefluid orifices are of maximum cross section when the rod end is out ofthe bore and gradually diminish in cross section as the rod end movesinto the bore.

A cushion piston 80, which I call a floating piston, is freely slidablein piston chamber 52. Preferably piston 80 is an annulus with a centralcylindrical bore 81 slidable on the cylindrical face 82 of valve rod 71there being suitable O ring, or other seals, 83 on the exterior andinterior thereof to prevent leakage of fluid thereby while permittingthe piston to slide in the chamber and on the rod. Each opposite face 84and 85 of the piston 80 is provided with grooves 86 or 87 extending fromthe bore 81 outwardly, the grooves preferably being radial. Similarlythe axially extending tapered grooves 75 and 76 of the valve 71 are ofpredetermined length such that when the piston and rod are at the farend of their paths, as shown in FIGURE 5, the shallow end of the rodgrooves and the adjacent piston grooves are always connected 'by acounter bore 88 or 89 to form a fluid passage of predetermined reducedcross section. Thus influent fluid in port 45 can always pass along arod groove, out a radial groove to exert pressure on the adjacent faceof the piston.

Each adjusting screw 62, or 63, includes an annular shoulder 90, alocking nut 91 and a terminal tip 92 which serves as an adjustable stopfor controlling the length of travel of the valve rod 71 at eachopposite end of its path. The screws 62 and 63 are shown in minimumstroke condition in FIGURE with the tapered grooves 76 just reaching toradial grooves 86. This position provides maximum cushioning effect fora minimum time period. Tightening of the screws 62 and 63 toward eachother will reduce the length of the stroke of the rod 71, increase theminimum size of the orifices and reduce the cushioning effect, andincrease the time of operation correspondingly.

Because of the provision of the fixed orifice of minimum size, explainedabove and designated 93 in FIG- URE 5, the cushion piston 80 and valverod 71 never totally close the orifices entirely in the manner of acheck valve but simply change orifice size between a predeterminedmaximum area and a predetermined minimum area. Thus the impact and shockof total closure is eliminated.

As shown diagrammatically in FIGURE 1, the pump 21 is forcing thehydraulic fluid in the direction of the full headed arrows to forcepiston 24 to the left and hold cushion piston 80 and valve 71 at theleft end of the cushion cylinder so that full pressure is being exertedon the work piston. The half headed arrows represents flow of the fluidback toward the pump and reservoir. The fluid pressure has moved thevalve 71 to the left by pressure exerted against the tapered bottom ofthe grooves 75 and moved the cushion piston to the left by pressure onthe face 85. The flow passage at 93 is open, but back pressuretherethrough against the face 84 of piston 80 is minimal.

In FIGURE 2 the system 20 is illustrated diagrammatically with thecontrol mechanism 38 suddenly shifted from the position of FIGURE 1 inwhich piston 24 is advancing, to a position in which the flow isstopped, or reversed, the piston 24 being intermediate of its cylinder23. As shown by the full headed arrows, the pump 21 is now exertingpressure on the opposite face of work piston 24 to thrust it to theright and in conventional systems shock would be great. However, in thesystem of this invention, the pressure exerted by the pump 21 in conduit32 has been partly diverted into the conduit means 43, into infiuentport 45 and against valve 71 to push the valve entirely to the right andto push the cushion piston toward the right. The cushion piston nowreceives all of the shock pressure, this pressure forces piston 80 tothe right and expels fluid through the orifice now established by valve71 which is hearing against the face 92 of adjusting screw 63. Theeflluent hydraulic fluid is thus expelled through orifice 75, port 46and conduit 44 to enter the main system to flow through conduit 44 orconduit 37 as the need of the system demands.

As shown in FIGURE 3 the valve 71 is maintained by pump pressure fullyto the right, cushion piston 80 has moved further to the right, and allshock forces have been absorbed to permit the decelerated work piston totravel to the right.

In FIGURE 4 the work piston is shown continuing to travel to the right,or retract, while the remote hydraulic cushion assembly is in stand-byposition waiting another change of flow direction.

I claim:

1. In a hydraulic system of the type comprising a hydraulic pump forgenerating force; a double acting work cylinder having a piston forperforming mechanical work; hydraulic conduits connecting each oppositeend of said cylinder with said pump and control mechanism, associatedwith said pump, for selectively stopping, or reversing, the flow ofincompressible hydraulic fluid filling said system, the combination of:

a remote, hydraulic cushion assembly for reducing shock to said systemcaused by stoppage, or direction change, of a loaded piston at anylocation along said cylinder, said assembly comprising:

a double acting, cushion cylinder having a centrally disposed pistonchamber therewithin, and having a pair of valve bores, each bore openinginto said chamber at an opposite end of said cylinder;

conduit means connecting each said bore with one of the ends of saidwork cylinder;

21 double acting valve axially slidable in said cushion cylinder, eachopposite end thereof having means forming orifices in cooperation withone of said bores for throttling flow from said piston chamber to theadjacent conduit means, and

a piston axially slidable in said piston chamber, said piston beingcooperable with said valve to create progressively diminishing backpressure on the piston of said work cylinder when flow in said system isstopped or reversed in direction.

2. A hydraulic system as specified in claim 1 wherein said double endedvalve is a cylindrical rod with tapered, grooved ends and said bores areeach cylindrical, said grooves and bores forming said orifices and saidorifices becoming progressively smaller as each end of said rod movesfurther into its bore.

3. A hydraulic system as specified in claim 1 wherein said double actingvalve is a cylindrical rod and said piston is an annulus slidable onsaid rod.

4. A hydraulic system as specified in claim 1 wherein said piston is anannulus axially slidable on said valve, each said valve end is axiallygrooved and each opposite face of said piston is radially grooved andcounter bored to register therewith for providing a permanent fluidpassage of predetermined cross section from each opposite end of saidpiston chamber to the adjacent conduit means.

5. A hydraulic system as specified in claim 1 plus means at eachopposite end of said cushion cylinder for adjusting the length of thestroke of said valve to thereby adjust the size of said orifices.

6. In a positive displacement hydraulic system having a double acting,work cylinder, a source of hydraulic fluid under pressure and controlmechanism for reversing flow of said fluid the combination of:

a double acting cushion cylinder mounted in said system in parallelismwith said work cylinder, said cushion cylinder having a piston chamberwith a fluid port at each opposite end thereof connected to thecorresponding end of said work cylinder;

a piston floatingly mounted within said chamber for free axial movementtherealong from proximate one said port to proximate the other saidport, and

throttle valve means including orifices associated with each said port,said means being operable, to progressively diminish flow through theport approached by said piston and to correspondingly increase flowthrough the other said port.

7. A hydraulic system as specified in claim 6 wherein said double actingcushion cylinder includes adjustment means at each opposite end thereof,for varying the efiective cross sectional area of the orifices of saidthrottle valve means.

8. A hydraulic system as specified in claim 6 wherein said throttlevalve means is a rod having axially extending, tapered grooves in eachopposite end, each end closely fitting, and being slidable, in a bore ateach opposite end of said chamber to define a series of said orificestherearound leading to one of said ports whereby influent fluid movesthe adjacent end of said rod out of its bore to increase the size of theorifices at that end while the other end of said rod is moved into itsbore to decrease the size of the orifices at said other end.

9. A reversible, hydraulic cushion cylinder for use in a closed,hydraulic, reversible pump and motor system port.

References Cited by the Examiner UNITED STATES PATENTS 845,827 3/1907Steedman 91-396 2,389,654 11/1945 Van Der Werif 91--42O 2,753,849 7/1956Becker 9l38 2,935,051 5/1960 Fuller et al 9285 X 2,965,074 12/1960Williamson 92--8 X EDGA-R W. GEOGHEGAN, Primary Examiner.

SAMUEL LEVINE, Examiner.

A. S. ROSEN, Assistant Examiner.

1. IN A HYDRAULIC SYSTEM OF THE TYPE COMPRISING A HYDRAULIC PUMP FORGENERATING FORCE; A DOUBLE ACTING WORK CYLINDER HAVING A PISTON FORPERFORMING MECHANICAL WORK, HYDRAULIC CONDUITS CONNECTING EACH OPPOSITEEND OF SAID CYLINDER WITH SAID PUMP AND CONTROL MECHANISM, ASSOCIATEDWITH SAID PUMP, FOR SELECTIVELY STOPPING, OR REVERSING, THE FLOW OFINCOMPRESSIBLE HYDRAULIC FLUID FILLING SAID SYSTEM, THE COMBINATION OF:A REMOTE, HYDRAULIC CUSHION ASSEMBLY FOR REDUCING SHOCK TO SAID SYSTEMCAUSED BY STOPPAGE, OR DIRECTION CHANGE, OF A LOADED PISTON AT ANYLOCATION ALONG SAID CYLINDER, SAID ASSEMBLY COMPRISING: A DOUBLE ACTING,CUSHION CYLINDER HAVING A CENTRALLY DISPOSED PISTON CHAMBER THEREWITHIN,AND HAVING A PAIR OF VALVE BORES, EACH BORE OPENING INTO SAID CHAMBER ATAN OPPOSITE END OF SAID CYLINDER;